It is well known in the art that guard rings and the like can be diffused into the substrates of silicon semiconductor devices (and especially silicon power devices) for purposes of terminating or separating devices on a common substrate. However, devices formed on silicon carbide (SIC) substrates cannot be terminated using diffused guard rings because of the very small diffusion coefficients of conventional dopants in SiC. Use of field plates on SiC substrates is also limited since high electric fields in the dielectric and the subsequent breakdown of the dielectric is likely to occur before avalanche breakdown of the SiC.
In particular, the power performance of present SiC diodes is limited by high reverse leakage current. The leakage current in SiC Schottky diodes and p-n diodes, for example, is two orders of magnitude higher than the reverse leakage current in silicon diodes or rectifiers. In many instances the prior art uses thermally grown oxide as a field termination, which is an extremely slow process and provides unreliable results.
In the fabrication of semiconductor devices, it is known that damaging the substrate in an area surrounding a gate contact with implants of electrically inactive ions affects the electrical field along the surface of the substrate and, hence, the breakdown voltage of the device. See for example, U.S. Pat. No. 5,399,883, entitled "High Voltage Silicon Carbide MESFETS and Methods of Fabricating Same" issued Mar. 11, 1995. In all of these prior art devices, the damaged area extends at least from the gate electrode to the drain electrode, and in some devices the damage region also extends to the source electrode.
The ion implantation damage is the most successful electric field termination structure to date. Additionally, it has been found that annealing the implant at a temperature below 400.degree. C. helps to reduce the reverse leakage current. However, when the implant is annealed at temperatures in excess of 400.degree. C. the damage starts to be removed from the crystalline structure, thus decreasing the effectiveness of the termination.
Also, all of these prior art devices, in actual practice, have relatively large reverse leakage current and a soft-breakdown. Accordingly, it would be highly advantageous to provide a method of fabricating silicon carbide rectifiers and other semiconductor devices using Schottky contacts with an improved reverse breakdown characteristics.
It is a purpose of the present invention to provide a new and improved method of fabricating semiconductor devices.
It is another purpose of the present invention to provide a new and improved method of fabricating semiconductor devices including a Schottky diode or contact.
It is still another purpose of the present invention to provide a new and improved method of fabricating semiconductor devices including a Schottky diode or contact with improved reverse breakdown characteristics.
It is yet another purpose of the present invention to provide a new and improved method of fabricating semiconductor devices including a Schottky diode or contact on silicon carbide substrates with improved reverse breakdown characteristics.
It is a further purpose of the present invention to provide new and improved semiconductor devices including Schottky diodes or contacts.
It is still a further purpose of the present invention to provide new and improved semiconductor devices including Schottky diodes or contacts with improved reverse breakdown characteristics.
It is yet a further purpose of the present invention to provide new and improved semiconductor devices including Schottky diodes or contacts on silicon carbide substrates with improved reverse breakdown characteristics.